This invention relates to the mechanical wave heating of residual hydrocarbons in partially exhausted oil wells, or other viscous hydrocarbons located underground, for the purpose of reducing their viscosity and thus facilitating their extraction.
Liquid petroleum is conventionally obtained by drilling into oil-bearing strata, the bore-hole being lined with steel pipe which typically is from four to ten inches in inside diameter. Where the bore-hole passes through oil bearing sand or porous rock layers, the walls of the pipe are pierced to permit the oil, under the formation pressure, to flow into the pipe and so to the surface. Water is conventionally injected into the formation at high pressure through adjacent wells, and when the natural artesian pressure of the formation becomes insufficient this added pressure serves to force the oil to the surface. The depth of the wells typically ranges from 1500 to 15,000 feet or more. This method generally serves to extract of the order of one-third of the deposit, the remaining two-thirds being too viscous to flow at the temperature of the formation. Several methods are now in use to salvage part of this residue. These include injection of steam into the oil-bearing formation, and although costly this serves to recover perhaps another 15 to 20 percent of the deposit. Other methods that have been used without marked success include injection of solvents, electrical conduction heating, and heating by combustion of the formation, brought about by injecting air or oxygen.
At best the application of any known method of secondary recovery results in the raising of the recovery proportion from about one-third to about one-half, and in many cases at an uneconomical cost for this one-sixth of the deposit.
If a suitable heating technique were utilized in association with such "exhausted" liquid petroleum oil wells to raise the temperature of the residual underground petroleum deposits, the raising of the temperature of these deposits would be expected to reduce the viscosity of the petroleum to permit further recovery of petroleum from such wells could be economically realized. The problem heretofore experienced in the industry is that economically viable heating techniques have been difficult, if not impossible to realize in such wells. The residues are relatively inefficient thermal conductors, and of course it is necessary to heat an appreciable volume of the residues, without destruction or consumption thereof, if any given heating technique is to have any reasonable commercial prospects.